An important feature of many vertebrate retinas is their duplex organization; that is, a rod system effectively mediates vision at low light levels while cones are active at higher illumination levels. This proposal is concerned with the properties of each of these systems and the interactions between the two. Two unique experimental methods will be brought to bear on the problems we are addressing. We first wish to investigate the properties of each of the systems in isolation from the other. By using the methods of response-summation and sensitivity-summation, we will study how responses to separate stimuli are summed within each system and construct a model of the way separate signals are transformed and combined. We will also use the method of the analysis of the variability of firing rate to determine if the responses to the two stimuli are independent at the level of the "on" and "off" processes. The effects of adapting lights of different spatial configurations will also be examined with respect to the above analyses, so that the effects of both local and pooled adaptation may be studied. The same two methods will be brought to bear to study the interaction of the two systems to generate a model for the combination and interactions of rods and cones in various states of adaptation. The constraints imposed by this model, together with those of the models for the two systems studied separately, will enable us to synthesize a comprehensive model for the duplex retina. The responses of single ganglion cells will be recorded from the retinas of intact, self-respiring goldfish. This species has a typical duplex retina, and can serve as a model for vision in higher animals. These studies should yield general information about the processing of visual stimuli.